why STM32F407 descovery flashed software takes effect after replugging the cable

rocko874 said:

they say that its about the index variable being local

you've missed the point.

Did you follow the link I gave?

The compiler sees your loop as totally pointless, so is perfectly entitled to optimise it out.

It may help if you make the loop index volatile:

	while(1)
	{
	    volatile uint32_t i;
	    
		GPIOD->BSRR=(1uL<<15);
		
		for( i=0; i<500000; i++ ){}
        
        GPIOD->BSRR=(1uL<<(15+16));		


	}

rocko874 said:

they say that its about the index variable being local

you've missed the point.

Did you follow the link I gave?

The compiler sees your loop as totally pointless, so is perfectly entitled to optimise it out.

It may help if you make the loop index volatile:

	while(1)
	{
	    volatile uint32_t i;
	    
		GPIOD->BSRR=(1uL<<15);
		
		for( i=0; i<500000; i++ ){}
        
        GPIOD->BSRR=(1uL<<(15+16));		


	}

rocko874 said:

So every variable has to volotile now?

No - it's just a kludge to get your busy-loop delay working.

rocko874 said:

I tried to write a function with a loop and it canceled it in optimisation too

re-read the linked posts - you need to understand that this is expected behaviour when you write useless loops.

In particular: https://www.avrfreaks.net/comment/3078001#comment-3078001 - the bit, "what a 'C' program is actually about"